Broadband internet access to aerial platforms such as low altitude drones flying at an altitude of about 400 feet, and general aviation and commercial aircraft flying at altitudes of as high as 50,000 feet, has in recent years been of great interest. Two different approaches to providing broadband internet access to aircraft have been: a network of ground cell sites referred to as ATG (Air to Ground); satellite based aeronautical broadband access systems.
Communications systems using GSOs (Geo-Stationary Satellites) can provide ubiquitous internet access to aircraft over land as well as water. However, satellite-based systems are expensive means of providing broadband access to aircraft. ATG systems are a less expensive means of providing broadband access for aircraft flying over land. To provide ubiquitous and cost efficient broadband access to aircraft over land and oceans, a hybrid system consisting of a cost efficient ATG system for coverage over land, combined with a satellite-based system for coverage over water, is one candidate solution.
A well-known ATG system is the network of cell sites that is deployed and operated by Gogo in the 800 MHz band, and covers the CONUS (Continental US). This system has access only to 4 MHz of spectrum; this small amount of spectrum limits the data rate to each aircraft and the overall network throughput. In order to provide a high data rate and high throughput ATG system, larger amount of spectrum is needed. However, it is also important that the spectrum be inexpensive. Licensed spectrum that is usable for broadband access to smartphones and other consumer devices is too expensive to be used for ATG systems. Therefore, an inexpensive source of spectrum is needed for ATG systems.
There is a large amount of spectrum in frequency bands above 3 GHz. One source of spectrum for ATG service is the 5 GHz unlicensed band, specifically the so called UNII-1 (5.15 to 5.25 GHz) and UNII-3 (5.725 to 5.85 GHz) bands. The obvious benefit of using the unlicensed bands is that they do not require any license fees. However, since the spectrum is being used by multiple systems, techniques must be devised to mitigate interference from other systems into the ATG system, while meeting the FCC imposed EIRP (Effective Isotropic Radiated Power) limits in the unlicensed bands. There are also other sources of spectrum above 5 GHz such as the C band, or even higher bands, where an ATG system may be able to share the spectrum with another service. Signal attenuation due to propagation path loss and other atmospheric effects are high in higher frequencies, and techniques are required to mitigate these effects. Moreover, the objective is to provide very high data rates to the aircraft, similar to the data rates to which people are accustomed at home. Therefore, system and methods are required to develop a high throughput system specifically optimized for aerial platforms.